1. Field of the Invention
This invention relates to an acrylic fiber precursor for making carbon fibers which has specific surface characteristics and has a dense inner structure, a method for making said acrylic fiber precursor, a method for making high performance carbon fibers free from fiber defects such as fusion bonding or agglutination from said acrylic fiber precursor and the carbon fibers made thereby.
2. Discussion of the Background
Carbon fibers made from acrylic fiber precursors have high performance and have been used in various fields such as secondary structural materials in aircraft. However, the higher performance carbon fibers are strongly demanded for use as primary structural materials.
Development for making carbon fibers which satisfy such demand has been made and acrylic fiber precursors with a smooth surface have been developed for this purpose. These precursors have a dense structure free of inner voids and considerably high performance carbon fibers can be obtained therefrom.
However, the precursors having high surface smoothness tend to cause undesirable phenomena such as fusion bonding or agglutination of filaments, which bring about defects in the carbon fibers made therefrom at the flameproofing step. For removal of these defects and obtaining precursors from which high performance carbon fibers can always be made, oiling agents used for treatment of these precursors have been carefully selected so as to prevent said fusion bonding or agglutination phenomena at the calcination step of the precursors. However, in order to prevent said undesired defects by such method, there are naturally limitations and precursors which do not bring about the above undesired phenomena without careful selection of the oiling agents have been strongly desired for obtaining high performance carbon fibers.